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Well after stupidly starting this arugment and so reading through both pages, it seems you're argueing slightly diffferent points, it seems bountyhunter is saying it'll ONLY do damage if the battery is faulty, and therefore overloads the electrical system trying to make up the difference, and NOMAD is saying that the electrical system won't overcharge a battery at 14volts(ei correctly working battery) but bountyhunter is talking about a damaged battery, and it seems to me both you're points are correct and don't contradict each other.

btw yes, i'm bored..
 

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The Cruising Gunsmith
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Let me try and explain this one last time.
If jumping a bike/car/truck/ or whatever....it would take faulty regulator to allow more than14.5 volts
Which is irrelevant to my point: a car or bike uses a CV (constant voltage) charger which forces the system up to 14.5V by sourcing current into the battery from the alternator... if one of the cells is shorted, it is impossible to get the battery up to 14.5V and so it sources max current until the alternator burns out or the battery boils it's guts out from internal heating.

and most when they fail, undercharge, not overcharge.
Lead acid storage batteries do not fail from undercharge, their primary failure modes are:

1) sulfation which covers areas of the plates increasing the battery's internal impedance until it can't source enough current.

2) Cell short by sediment. The coating on the plates burns off and drops to the bottom over time, and can build up enough to short the cell. The loss of plate coating is proportional to how much the battery is discharged. The more you use it the faster you lose it.


And if you are going with the theory of a weak battery causing it to try to overcharge, then the cars battery would have to be bad as well as the bikes, or else the regulator would see an ok voltage from at least one of them.
You don't get the concept of putting two batteries in pararlell, do you? Whichever one is lower pulls them both down.

or else the regulator would see an ok voltage from at least one of them.
same comment

as for too much amperage, a battery takes what it wants, and then stops taking more, so the regulator stops sending more.
If one cell is shorted, you can pump all day long and it will still read zero volts. The other five cells can't get up to 14.5V.

So for this too happen both the car and bike batteyr have to be bad, as well as the regulator fail in a very uncommon way.
Gibberish

So I stand by my previous explanation.
Right

And as a ast comment before i stop looking and responding to this thread.
If the scenario placed before you by bounty held any water, then every time a car say had its lites left on and ran a battery down.
Then was jumped it would read low voltage and fry stuff.
If the battery is only discharged (and not shorted out) the cells would come up prettu fast due to a couple of things:

1) The battery in parallel would be sourcing a massive surge current into the dead battery since the discharged battery looks like a massive current sink until it charges up.

2) The discharged battery's dynamic impedance would allow the terminal voltage to get to 12V pretty quick.

You don't seem to comprehend the difference between a discharged cell (which can be charged up rapidly) and a shorted cell which can never be charged up to any voltage.

And, you can't comprehend the fact that a shorted cell in a stack of six cells will mean the battery is going to give a low voltage to the charging circuit even when the five good cells are severely overcharged to the point of damaging the battery.


Then was jumped it would read low voltage and fry stuff.
Jumping a stone dead battery can dmage the good battery, although it may not be immediately apparrent. lead acid storage cell's life span is proportional to how deeply they are discharged. The massive current dump to bring up a dead battery can take a good bite out of the good battery's life span.

And leaving the lights on and dumping a battery stone dead will definitely shorten it's life span.

And if say parked on a hill and bump started the car once started would read very low voltage since the battery is dead, and fry itself upon starting.
As I said, if the battery cells are still functional, the alternator can force the battery terminal voltage up to 14V within a relatively short time, even though it may take an hour to get to full charge.
 

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The Cruising Gunsmith
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Well after stupidly starting this arugment and so reading through both pages, it seems you're argueing slightly diffferent points, it seems bountyhunter is saying it'll ONLY do damage if the battery is faulty, and therefore overloads the electrical system trying to make up the difference, and NOMAD is saying that the electrical system won't overcharge a battery at 14volts(ei correctly working battery) but bountyhunter is talking about a damaged battery, and it seems to me both you're points are correct and don't contradict each other.

btw yes, i'm bored..
Maybe, but know this: battery cells can short and they can also burn open:

The battery functions as the charging system's "filter capacitor" to keep the pulsating DC voltage at the alternator a relatively smooth DC voltage.

One thing people don't realize is that if a battery cell blows open and they "bump start their car or bike", the electricals will work... for a while... but can be getting hit with high voltage spikes.

I kick started my bike one day when a flaky battery went south not knowing a cell was open. I got a block and noticed my brake light was gone, then the ignition went dead. The total damage was a couple of running lights, all the instrument lights, the brake light, and the CDI module.

The shorted cell can also be dangerous since it will overload the charging system and get very hot as the alterntor pumps massive current into it in a fruitless effort to get it up to the right voltage.

There are a couple of cases where a bump start does no damage:

1) if a cell has simply grown weak over time through sulfation and can't source enough current to start the car, a bump start will work because that weak cell can still be forced up to 2.2V allowing the total battery voltage to be correct. That cell has no current capability which means when you try to start the car again, it won't go.

2) If the battery was good and just killed by leaving the lights on, it will probably charge back up OK.
 

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OK so I made the same error ( after being told by someone it was OK to do, but didn't say whether car was running). Weak battery wouldn't start bike. I tried it with car off and it didn't work, cranked but no start, so I started car, still same.
Once disconnected jumper cables bike is totally dead. I had my battery tested and it is fine, but the bike is dead when I try and start, absolutely nothing.
Where do you think the problem may be?
 

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You could jumpstart a motorcycle from a nuclear aircraft carrier, as long as it is nominally 12VDC, (14VDC really) without any problems. If you did it right, the car battery will not cause any harm. Even when the car running, putting out 14 VDC, will not do it, as the motorcycle running will put out same voltage. I know I lot of people will say otherwise, they just don't understand the Kirckoff laws V = RI.

.....if you don't feel confortable with that, don't do it. If you understand electricity and do it right IT WILL NOT DO ANY HARM.

..
 
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